Production of paper products such as paper towels, tissues, napkins, and the like often employ the use of several manufacturing steps. One of these manufacturing steps involves the application of a substance onto the web from which the paper product is made. The purpose of applying a substance onto the web is due to a desire to change the functional properties of the resulting paper product. For instance, the substance may be a strength agent, a softening agent, or a debonding agent, or any other substance which affects the functional properties of the product. Application of these types of substances to a web will result in the final paper product having desired characteristics. Typically, strengthening agents are added to a web that is made into paper towels in order to provide for a paper towel that will not disintegrate upon contact with water or other liquids. Alternatively, debonding agents are sometimes applied to a web that is made into toilet tissue such that the resulting product will break up upon contact with water. As such, the application of a substance that modifies the functional properties of a paper product is an important step in the manufacturing these products.
One method known in the art that is used to apply a substance onto a web is known as direct printing. Direct printing can employ flexographic, gravure, or ink jet technology. Ink jet technology includes a device known as an ink jet print head that has a plurality of orifices. A substance may be expelled from one or more of these orifices thus exiting the print head of the ink jet printer. Drops of the substance then travel a throw distance between the print head and the web or other surface onto which the substance is to be applied. The orifices of the print head may be aligned in a single row or may be formed having various patterns. The substance may be expelled from these orifices either simultaneously or through selected orifices at any given time. Although ink jet technology is commonly used in ink printers which apply printing to a paper, ink jet technology is also known in the art as a method of applying substances to a paper in order to effect the functional properties of the paper.
Direct printing may sometimes employ a guide roll onto which the moving web is contacted. The ink jet print head may then apply the substance onto the web as the web is rolled over the guide roll. Alternatively, a transfer roll may not be present in direct printing. Here, the ink jet print head applies the substance to a moving web that is stretched in between two points, for instance two other rolls. The moving web may create a layer of boundary air that is approximately one-half inch to one inch in distance from the surface of the moving web. Although, it is to be understood that in the present invention that any size of boundary air may be present and the invention is not limited to any particular distance. This boundary air is a turbulent airflow that has a significant amount of dust present. The dust is formed by the particles that create the web. In ink jet printing, the throw distance from the print head to the surface onto which the substance is applied is typically less than fifteen millimeters, and is commonly less than five millimeters. Therefore, in direct printing the print head is typically within the boundary air. It is often the case that the dust will build up on the print head of the ink jet printer due to static effects. This buildup of dust on the print head can significantly impact the dispensing of the substance from the ink jet printer. For instance, several of the orifices can become jammed or partially clogged therefore preventing the desired distribution of the substance onto the web. Additionally, a reduced amount of substance can be applied from that which is desired.
The production of paper products typically occurs at a fast rate. Therefore, the web is moved at a high rate of speed producing boundary air which is also moving at an elevated speed. Due to the fact that ink jet technology propels drops of the substrate onto the web, this fast moving boundary air can potentially cause problems. For instance, the boundary air may act as a barrier to prevent the drops of the substrate from reaching the web. In addition, the boundary air may effect the location onto which the substance is placed on the web causing a buildup on some parts of the web and leaving other parts of the web with none or a reduced amount of the substance. In most circumstances, such an uneven dispersion of the substance is undesired. Additionally, the buildup of dust on the ink jet print head can cause the formation of satellite drops which are smaller drops of the chemistry that are formed due to drop break-up upon impact with dust or due to improper drop formation. These satellite drops are smaller and have a greater potential of being swept away by the boundary air and/or being inhaled by a person in the proximity of the printing equipment. These problems exist at relatively low speeds of a moving web, such as speeds less than 500 feet per minute, but become worse at higher speeds.
Although it is possible to move the ink jet print head away from the boundary air such that the problem of dust buildup is not as severe, this modification causes other side effects. First, the ink jet print head is designed to operate at relatively small throw distances. Having a larger throw distance will result in a loss of resolution of the substance applied to the web. For instance, more overlapping of the substance applied to the web will occur. Additionally, the substance has a greater chance of being swept away due to the boundary air. The exact placement of the substance onto the web will not be controllable since the distance the drop of the substance is thrown will be great and will be through a turbulent airflow.
Various features and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the present invention.
The present invention provides for an offset print apparatus for applying a substance to a moving web. The offset print apparatus includes a transfer roll that is capable of being rotated. A moving web is provided and is in contact with a first circumferential portion of the transfer roll. The moving web moves over or under the transfer roll and stays in contact with the first circumferential portion of the transfer roll while moving over the transfer roll. A dispenser is located proximate to a second circumferential portion of the transfer roll and has at least one orifice. A substance may also be present and be dispensed from the dispenser through the at least one orifice. The substance is dispensed onto the transfer roll without having the dispenser contact the transfer roll. The transfer roll rotates the substance into engagement with the moving web such that at least a portion of the substance is applied to the moving web.
The present invention also provides for an offset print apparatus for applying a substance to a web that includes a transfer roll. An ink jet printer is provided that has a print head located proximate to the transfer roll. The print head has a plurality of orifices from which the substance is dispensed onto the transfer roll. The distance between the surface of the print head and the transfer roll is defined as a throw distance. A web contacts the transfer roll such that the substance that is dispensed onto the transfer roll is transferred to the web through contact of the transfer roll and the web. The web has an amount of dust laden boundary air that is formed proximate to the web when the web is moving. The print head of the ink jet printer need not come into contact with the dust laden boundary air that is formed when the web is moving.
The present invention also encompasses an apparatus as discussed above where the substance is applied to affect the functional properties of the web.
A further exemplary embodiment of the present invention is provided as an apparatus as immediately discussed where the substance is selected from the group that consists of but is not limited to strength agents, softening agents, and debonding agents.
A further exemplary embodiment of the present invention exists in an apparatus as previous discussed where the dispenser is an ink jet printing apparatus.
Alternatively, the present invention includes an offset print apparatus as previously discussed which further has a doctor blade that is located proximate to the transfer roll. The doctor blade removes any of the substance that remains on the transfer roll after engagement of the substance with the moving web.
Alternatively, the present invention includes an apparatus as set forth above where the moving web is moving at a speed of between about 5,000 feet per minute and about 8,000 feet per minute in one exemplary embodiment, and a speed between about 500 and 3,000 feet per minute in another exemplary embodiment.
Additionally, the present invention includes an exemplary embodiment of an offset print apparatus as discussed above where the throw distance is between about 2 and about 3 millimeters in one exemplary embodiment, and can be between 1 and 20 millimeters in other exemplary embodiments.
Another exemplary embodiment of the invention exists where the print head is spaced away from and not in contact with the boundary air that is formed by the moving web.
The present invention also encompasses a method for applying a substance to a moving web. The method includes the step of rotating a transfer roll. A web is moved over or under a first circumferential portion of the transfer roll. The web stays in contact with the first circumferential portion while being moved over or under the transfer roll. A dispenser is located proximate to a second circumferential portion of the transfer roll. The dispenser is located such that boundary air from the moving web is substantially remote from the dispenser. A substance is dispensed from the dispenser onto the transfer roll at the second circumferential portion. The substance is rotated into engagement with the moving web so that at least a portion of the substance is applied to the moving web.